"I went to Best Buy [and] looked at the price," Lising says. "I was like, 'Ehh — I'm sure I can find this cheaper online.' "

So he whipped out his smartphone and scanned the barcode, found it cheaper and ... no sale for Best Buy.

There's a word for that kind of in-store comparison shopping: "showrooming."

Bryan Wargo, co-founder of a startup called Nearbuy Systems, says everyone in retail "knows they're being showroomed. But they don't know by who, for what products, when it's happening [or] what kind of consumer does that."

A mobile shopping revolution is under way, and brick-and-mortar retailers are worried.

Consumers using smartphones and tablets are changing the way stores market, set prices and track customer tastes — leaving mobile technologies poised to roil the $4 trillion U.S. retail industry.

Learning More About Brick-and-Mortar Shoppers

When you shop online, marketers are following your every click. But when you walk into a store they know almost nothing about you.

That detailed information about in-store shoppers is exactly what retailers want.

Wargo's company is using mobile technology to try to give it to merchants. Inside a drafty warehouse in Menlo Park, less than a mile from Facebook's sprawling new headquarters, Nearbuy has created a mockup of a big-box retail store.

There are fake shelves — the floor is laid out in a grid with blue masking tape — and there's a network of security cameras overhead. But instead of tracking real customers around the space, they're tracking a group of little robots.

Wargo and Nearbuy co-founder and Chief Technology Officer Marc Jamtgaard are using their technology to track the Stormtroopers — or real people — to within a couple feet of where they're standing.

"It's tracking my iPhone right now, so it is using Wi-Fi, which gives us about 10 meters of accuracy," Jamtgaard says. And because Wi-Fi is often imprecise, "we are augmenting that with the video surveillance system that is in this warehouse," Jamtgaard says.

"Our challenge was, take what we already have, and most stores have — Wi-Fi and ... video for security and things — and mix those two signals together to create something that is more accurate," Wargo says.

Retailers could use this technology to build apps to guide customers through their store aisles to specific products, or even deliver discounts and coupons based on where people are standing in any particular store.

"The vision everyone has for this technology is that you walk in front of the soda. And then Coke and Pepsi in the background are going to bid up to see who can send you that coupon," Wargo says.

This kind of technology could also let stores know if you are on your phone checking prices — or even buying something from a competitor.

In other words, it could give those retailers who are being showroomed a fighting chance to win back your business before you walk out.

In short, it could save you money.

But, as Wargo says, "people need to opt-in. People need agree to be tracked or provide location-based services, or else we're not going to do it."

Ask says most new mobile shopping apps are making more or less the same bargain with their customers, trying to strike a balance between using the information they're collecting "in a way ... that makes me smile and say, 'Yeah, you know, I'm having a better day; I like this,' — versus something that seems creepy, as if I am being watched or followed," she says.

And when companies get this trade-off right, she says, consumers love it. She's totally comfortable, for example, scanning her prescriptions into a mobile app created by Walgreens. "It's about refilling a prescription in less than 20 seconds," she says.

Back at the Stanford mall, Lising and his friends agree. They like the idea of the Fandango app that tracks users everywhere they go, to tell them nearby movies that will start within an hour. "That would be helpful for sure," they say.

Like Lising, most customers are comfortable giving up all sorts of sensitive information if they feel like it is being used to help them — and if they believe it's not going to be abused.

So right now, brick-and-mortar stores are trying to figure out ways to get all of us to share more and more personal details through our mobile devices as we shop.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

MELISSA BLOCK, HOST:

This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.

ROBERT SIEGEL, HOST:

And I'm Robert Siegel. Now, a dispatch from the front lines of the mobile shopping revolution. Consumers armed with smartphones and tablets are changing the way stores market set prices and track customer tastes. And as NPR's Steve Henn reports, brick-and-mortar retailers are worried.

STEVE HENN, BYLINE: Best Buy lives in fear of this guy.

AVE LISING: My name is Ave.

HENN: Ave Lising and a group of his friends were walking through Stanford Mall last week, their cell phones clutched to their hands. Recently, Lising was shopping for a video game.

LISING: Went to Best Buy, looked at the prices. Like, yeah. I'm sure I could find this cheaper online.

HENN: So he whipped out his smartphone and scanned the bar code.

LISING: Found it cheaper, so...

HENN: There's a word for this kind of in-store comparison shopping.

BRYAN WARGO: People are being what's called show-roomed.

HENN: Bryan Wargo is co-founder of a start-up called Nearbuy Systems.

WARGO: Everyone knows they're being show-roomed, but they don't know by who, for what products, when it's happening, what type of consumer does that.

HENN: When you shop online, marketers are following every click, but when you walk into a store, they know almost nothing about you. What retailers want is information and inside a drafty warehouse in Menlo Park, less than a mile from Facebook's sprawling new headquarters, Wargo's company is using mobile technology to try and give it to them.

WARGO: It's tracking my iPhone right now, so it's using Wi-Fi, which gives up about 10 meters of accuracy.

MARC JAMTGAARD: Wi-Fi can make large errors and so we're augmenting that with the video surveillance system that's in this warehouse.

WARGO: So our challenge was, take what we already have - and most stores have Wi-Fi and they have video for security and things - and kind of mix those two signals together to come up with something that's more accurate.

HENN: Wargo and Jamtgaard have created a mock-up of a big box retail store. There are fake shelves. The floor is laid out in a grid with blue masking tape and there's a network of security cameras overhead. But instead of tracking real customers around this space, they're tracking a group of little robots.

Like one of those little vacuum robots?

JAMTGAARD: It's not quite the vacuum robot, but it's a little - it has a Web interface and a little video camera so you can see where you're going and you can drive around.

Wargo and Jamtgaard use this technology to track their stormtroopers - or real people - to within a couple of feet of where you're standing. Retailers could use this to build an app to guide customers through their store aisles to specific products or even deliver discounts and coupons based on where you're standing in any particular store.

JAMTGAARD: The vision everyone has for this technology is that, you know, you walk in front of the sodas and then Coke and Pepsi in the background are going to bid up to figure out who can send you that coupon.

HENN: This technology could also let stores know if you're on your phone checking prices or even buying something from someone else. It could give those retailers who are being show-roomed a fighting chance to win back your business before you walk out. It could save you money, but Wargo says...

WARGO: People need to opt in. People need to agree to be tracked or help provide location-based services or we're not going to do it.

JULIE ASK: I think you're really walking a fine line there.

HENN: Julie Ask is a mobile marketing guru at Forrester Research. She says most new mobile shopping apps are making more or less the same bargain with their customers.

ASK: Between how you use the information that you have about consumers that you've collected in a way that seems helpful, that adds value, that makes me smile and say, yeah. You know what? I'm having a better day. I like this. This helps me today versus something that seems very creepy, as if I'm being watched or followed.

HENN: Ask says, when you get this trade-off right, consumers love it. She's totally comfortable scanning her prescriptions into a mobile app created by Walgreens.

ASK: This is about refilling a prescription in less than 20 seconds.

HENN: Back at the Stanford Mall, Ave Lising and his friends agree. Fandango has an app that tracks your location everywhere you go.

LISING: And it'll tell you movies starting within an hour nearby you.

UNIDENTIFIED MAN: Which is cool. That would be helpful, for sure.

HENN: Most customers are pretty comfortable giving up all sorts of sensitive information, or not so sensitive information, if they feel like it's being used to help them and believe it's not going to be abused. So, right now, brick-and-mortar stores are trying to figure out ways to get all of us to share more and more personal details through our mobile devices as we shop.